A fluid dynamic bearing device supports a rotating member in a non-contact state by a dynamic pressure effect of a fluid created in a bearing clearance between a fixed member and the rotating member. This type of bearing device has characteristics of high-speed rotation, high rotation accuracy, low noise and the like, and is preferably used as a bearing device for a motor mounted on various types of electric equipment including information equipment, more specifically, as a bearing device for a spindle motor of a disk drive in a magnetic disk device such as HDD, an optical disk device such as CD-ROM, CD-R/RW, and DVD-ROM/RAM, and a magnetic optical disk device such as MD and MO, or as a bearing device for a motor such as a polygon scanner motor of a laser beam printer (LBP), a color wheel motor of a projector and a fan motor.
For example, in a fluid dynamic bearing device incorporated in a spindle motor of a disk drive device such as HDD, there is known one in which both a radial bearing part supporting a shaft member in a radial direction and a thrust bearing part supporting the same in a thrust direction are made of fluid dynamic bearings. As the thrust bearing part in this type of the fluid dynamic bearing device, there is known one in which dynamic pressure grooves as a dynamic pressure generating part are formed, for example, in either of an end surface of a flange part making up the rotating member and a surface opposed to this, for example, a lower end surface of a sleeve part making up a fixed member and an upper end surface of a bottom part of a housing (thrust bearing surface), and a thrust bearing clearance is formed between both the end surfaces (e.g., refer to Patent Document 1).
Moreover, in this fluid dynamic bearing device, normally, in order to prevent a lubricating oil injected into an internal space of the housing from leaking to the outside, a seal member is disposed in an opening part of the housing communicated to a radial bearing clearance. Therefore, a seal space formed between the seal member and the rotating member (e.g., a shaft member) is often formed on one end side in an axial direction of the radial bearing clearance (e.g., refer to Patent Document 2).
Moreover, with a recent trend toward enhanced portability and downsizing of information equipment, demands for downsizing and reduction in thickness to a fluid dynamic bearing device mounted on such information equipment or the like have also been increased.
As this type of fluid dynamic bearing device constituted so as to achieve reduction in thickness, for example, there is a fluid dynamic bearing device described in Japanese Patent Application Laid-Open No. 2005-315408. This is characterized in that a seal space, which in many conventional cases, has been provided on one end opening side of a fixed member, in other words, on one end opening side of a radial bearing clearance, is formed radially outside of the radial bearing clearance, which reduces an axial dimension of the fluid dynamic bearing device by the seal space. In this case, a thrust bearing clearance is often formed between a lower end surface of a hub forming the seal space between an outer circumferential surface of the housing and the hub, and an upper end surface of the housing opposed to this.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-239951
[Patent Document 2] Japanese Patent Application Laid-Open No. 2003-65324
[Patent Document 3] Japanese Patent Application Laid-Open No. 2005-315408